The present invention generally relates to a technical field of a flat display device, and more particularly to a display device using an inorganic luminescent layer.
Presently, a display device or a light emitting device is being developed using an organic EL element.
However, there is a problem when an organic material is used as the organic EL element in that the material deteriorates due to moisture or the like, and has a short life time. In addition, due to its weakness against damage, an organic layer of the organic EL element cannot be deposited by sputtering; and it is also difficult to use a sputtering method for a film to be formed on the organic layer.
Further, when a color display panel is produced, it is necessary to form organic films of different materials corresponding to three colors; and it is difficult to increase the size of the area and there is a problem in that the display device becomes expensive.
An inorganic material used for an inorganic EL element is superior to that of the organic EL in terms of a longer life. Further, the inorganic EL can select many kinds of deposition methods (such as, sputtering or the like) because of its strength against damage and can easily deal with a large-size substrate.
However, a conventional inorganic EL needs to be applied with a voltage of about 100 V for light emission and cannot be controlled with a drive circuit (such as, a thin-film transistor or the like).
Although there is a document disclosing that a display has been produced with the use of an inorganic EL element driven by a thin film transistor, a high voltage is required and a mass production technology for this display has not yet been accomplished; and thus, the inorganic EL has not been used for a high resolution display or the like.
Recently, an inorganic EL material has been developed, which is capable of light emission at a lower voltage than in the conventional technique (Patent document 1). Specifically, it is known that an inorganic EL material containing ZnS emits light with a high brightness at a voltage of several volts (lower than ten volts), and the material is expected to have the possibility of a light emission control by the thin-film transistor due to the low voltage; and a color display device using a white inorganic EL and a color filter is expected to be mass-produced because of the high brightness. See, patent document No. JP A 2005-336275.